This application claims the priority of German application 198 22 730, filed in Germany on May 20, 1998.
The invention relates to a suspension system for the front wheel of a motorcycle, comprising a ball joint fork, which is rotatably and swivellably connected with the vehicle frame; a suspension element which is connected with the vehicle frame and by way of a ball joint is connected with a lower fork bridge; and spring elements which are supported on a movable part of the suspension system and on the vehicle frame.
A suspension system of this type is described in German Patent Document DE 41 10 954 A1. In the case of this known suspension system, the suspension element is constructed as a longitudinal control arm which is swivellable about a transverse axis connected at the rearward end with the vehicle frame.
In the case of this type of a suspension system, the forward bearing point of the longitudinal control arm, specifically the ball joint on the lower fork bridge, during the compression of the front wheel, moves along an arc of a circle about the rearward bearing point of the longitudinal control arm. The path of motion of the ball joint therefore has a horizontal component which is a function of the swivelling angle of the longitudinal control arm. The circumstance that this horizontal component changes during the compression of the front wheel is, however, disadvantageous for the suspension performance. It was therefore attempted to construct the longitudinal control arm as long as possible so that the radius of the path of motion of its forward bearing point is as large as possible and its curvature is therefore as small as possible. However, the length of the longitudinal control arm is constructively limited, particularly when the engine extends far to the front.
It is an object of the invention to further develop the suspension system of the above-mentioned type such that an optimal path of motion of the ball joint of the lower fork bridge can be achieved during the compression.
According to the invention, this object is achieved in that the suspension element is constructed as a central suspension element with a linear suspension function and is rigidly fastened to the forward frame of the motorcycle.
A longitudinal control arm can be eliminated in the case of the suspension system according to the invention. This also eliminates the costs connected with the development, storage and mounting of this component. Another advantage is the reduction of weight. By the selection of the inclination of the central suspension element, the path of motion of the ball joint fastened to the lower fork bridge can be influenced, and a path of motion can be achieved for which in the prior art a longitudinal control arm of considerable length would have been required. The suspension system according to the invention can also be used under narrow space conditions, for example, in the case of a motorcycle with an engine which projects far toward the front. The central suspension element is easily accessible for adjusting the suspension and the damping, and the chassis data and the kinematic characteristics can be changed without any major influence on the remaining vehicle.
The spring elements are preferably installed into the central suspension element.
The invention can be implemented in that the ball joint fork is constructed with a constant length and is swivellably and axially displaceably connected with an upper fork bridge. In the case of such a construction of the suspension, the spring elements or additional spring elements can be constructed as coil pressure springs which are supported on the upper fork bridge and on the ball joint fork.
However, the invention can also be implemented in that the ball joint fork is constructed as a telescopic fork and in that the lower fork bridge connects the two sliding tubes with one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.